Generally, electricity is produced by use of solar energy through a method of directly converting sunlight to electric energy and through a method of driving a generator as a heat engine using solar heat.
A solar power generator, which converts the sunlight directly to electricity, uses solar cells and is widely used because it is durable and easy to make the generation system semi-automatic or automatic.
However, this solar cell uses only a portion of sunlight in the range of visible and infrared rays, and low energy photon in long wavelength infrared ray cannot be used for electricity generation but increase the temperature of the solar cells, thereby lowering the efficiency of power generation. Moreover, the solar cells are expensive and have a significantly lower efficiency of power generation than the heat engines.
Meanwhile, a solar power generator driven by concentrated solar heat produces electricity using a heat engine such as turbine or Stirling engine that is driven by highly dense heat source, and has a higher theoretical efficiency of heat engine than the solar cells. Particularly, in order to drive the power generator using the solar heat, steam has to be generated to drive the turbine or the hot section of the Stirling engine has to be heated. The Stirling engine is a kind of external combustion engine that seals up operating gas, such as hydrogen or helium, in a space made with a cylinder and a piston and heats up and cools down this operating gas from the outside to reciprocate the piston to obtain mechanical energy. However, to drive the generator by operating such turbine or Stirling engine, the overall equipment becomes bigger and complicated, making it expensive to install and difficult to maintain and repair.